Conventionally, in a cement manufacturing facility 10 with a fluidized calciner, a raw material heated by heat exchange with hot gas in a suspension preheater 7 is discharged from a lower-stage cyclone 8 of the suspension preheater 7, and a portion of the raw material is dispersively loaded into a rotary kiln exhaust gas duct 9, with the remaining portion of the raw material supplied to a raw material supply chute 12 of a fluidized calciner 11 as depicted in FIG. 6.
In the fluidized calciner 11, high-pressure air is blown in through a fluidization air blowing port 13, an air chamber 13a, and an air dispersing plate 14 to form a fluidizing bed 15. At this time, the high-pressure air causes combustion of a portion of fuel supplied through a pulverized supply pipe 16, makes a calcination target raw material stagnant in the fluidizing bed 15 for a predetermined time, and then causes the raw material to fly up to a free board 17 located above the fluidizing bed 15. Furthermore, air from a hot clinker cooler 18 is sucked through a suction port 19 substantially in a tangential direction, and the fuel supplied through the pulverized coal supply pipe 16 is also combusted in the free board 17. Thus, the raw material loaded through the upper raw material supply chute 12 and the raw material flying up from a surface of the fluidizing bed 15 are efficiently and quickly calcined.
Then, all of the calcined raw material is entrained by calciner exhaust gas and enters a separating cyclone 21. On the other hand, the raw material dispersively loaded into the rotary kiln exhaust gas duct 9 is also partly calcined by rotary kiln exhaust gas and enters the separating cyclone 21 along with the rotary kiln exhaust gas. Moreover, a calcination raw material collected by the separating cyclone 21 is introduced into a rotary kiln 20 via a raw material chute 22.
On the other hand, hot air generated in the clinker cooler 18 is sucked into the rotary kiln 20 and the fluidized calciner 11 by a suction force of an induction fan 23. However, an excessive amount of hot air is sucked into the rotary kiln 20, which offers a low draft resistance. Thus, a part of the rotary kiln exhaust gas duct 9 is reduced in cross-sectional area, and the amount of hot air sucked into the fluidized calciner 11 is adjusted by using a damper 24.
In the fluidized calciner, a solid fuel such as coal is generally used as fuel that allows a cement raw material to be calcined. In particular, bituminous coal, which has high combustion quality, is micronized to fine powder for use. However, for effective utilization of limited resources, there has been a demand for the use of various types of fuel such as coal and oil coke, which have low combustion quality.
However, when pulverized coal of coal or coke, which has low combustion quality, is used as fuel, the rate of unburned fuel at an outlet of the fluidized calciner is high, and combustion occurs in the suspension preheater. As a result, the temperature in the preheater is elevated, and attachment is generated in the cyclone or the raw material chute. Thus, disadvantageously, occlusion frequently occurs in the preheater, hindering operation. Furthermore, in the fluidized calciner, the temperature and the concentration of dust are very high, making determination of a combustion state difficult.
Thus, Patent Literature 1 described below proposes a fluidized calciner for a cement raw material including: a tubular furnace body in which the axial direction of the tube is an up-down direction; an air dispersing plate provided substantially horizontally at a bottom portion of the furnace body and an air chamber below the air dispersing plate; a raw material supply chute located above the air dispersing plate and through which a raw material is supplied; a fuel supply nozzle located above the air dispersing plate and through which solid fuel is supplied to a fluidizing bed; a secondary air duct through which secondary air (extracted air) is supplied to above the air dispersing plate, in which the fuel supply nozzle is connected to the furnace body at a descending slope of 20° or more to a horizontal plane so as to be deflected toward a tangential side with respect to a centripetal direction.
This conventional fluidized calciner for a cement raw material calcines a raw material by combusting fuel. However, the connection position of the fuel supply nozzle and the like are based on empirical values, and this technique fails to take into account, for example, the presence or absence of the distribution of a raw material concentration or a gas concentration (particularly O2) in the fluidized calciner. Thus, when pulverized coal of coal or coke, which has low combustion quality, is used as fuel, there are disadvantages that sufficient calcination fails to be achieved and ducts may be occluded to hinder operation.
Furthermore, for refractories such as a furnace body, excessively high combustion quality disadvantageously causes the temperature near a furnace wall to be locally excessively elevated, leading to a high possibility of burnout.